1. Field of the Invention
The present invention relates to a multiple frequency band hybrid receiver, and more particularly, to a multiple frequency band hybrid receiver employing both homodyne (direct conversion) and heterodyne methods, in which at least one mixer is used in common in the signal processing according to both methods, whereby the total chip area required for the realization of the receiver can be reduced.
2. Description of the Related Art
As methods of converting a Radio Frequency (RF) signal to a baseband signal, a homodyne (direct conversion) method and a heterodyne method using an Intermediate Frequency (IF) have generally been known.
Multiple frequency band communications for receiving two or more signals usually employ a built-in front-end receiver including low noise amplifiers (LNAs) and mixers relative to the number of signals desired to be received. For example, a wireless local area network (WLAN) system employing IEEE 802.11n Standard is a dual-band system using both a 2 GHz band (IEEE 802.11b and IEEE 802.11g) and a 5 GHz band (IEEE 802.11a), so the WLAN system needs to have two built-in front-end receivers. When the WLAN system supports n number of multiple input multiple output (MIMO) units, the number of front-end receivers increases n times.
In order to enable communications using a currently used direct conversion method, an RF signal, amplified by an LNA, is inputted into a mixer such that its frequency is down-converted to a baseband frequency. This down-conversion needs a local oscillation (LO) frequency relative to a frequency range desired to be down-converted. As methods of generating an LO frequency inputted into a mixer, the direct generation, dual division, and dual multiplication of a voltage controlled oscillator (VCO) frequency have been known. The direct generation method may be problematic due to the pulling of the LO frequency. The dual division method requires a VCO oscillating at a frequency that is twice that of the required LO frequency, thereby causing difficulty in implementation. The dual multiplication method requires a separate phase shifter so as to generate in-phase and quadrature-phase (I/Q) signals. In general, when the IEEE 802.11n WLAN employs the dual division method, the VCO oscillates at 10 to 12 GHz and an LO signal of an RF band (5 GHz) is created, so there is a difficulty in the realization of the VCO and a phase locked loop (PLL).
Meanwhile, in the case of a heterodyne method, there is no need for a high frequency oscillation since an RF signal is not directly converted to a baseband signal, but is converted to an IF signal. For example, in the case that the IEEE 802.11n WLAN employs the heterodyne method, since it is unnecessary to oscillate at a very high frequency of 10 to 12 GHz, it is much easier to realize the VCO and the PLL, as compared to the direct conversion method. However, when a heterodyne mixer having a high IF is used, the high IF causes a difficulty in the design of the mixer and necessitate the use of an inductor or capacitor within the mixer or the addition of a separate band pass filter, whereby total chip area and production costs increase.